Vacuum pump

ABSTRACT

A heater  29  is mounted on the outer peripheral surface of a base  6  to heat the base  6 . A heat shutoff wall  24   b  is provided on a motor housing  24  to prevent the radiation heat of the base  6  heated by the heater  29  from transferring to a pump inside substrate  25 . A gap portion  27  is formed by providing a gap between the motor housing  24  and the base  6  to prevent the heat of the base 6 heated by the heater  29  from transferring to the motor housing  24 . Also, a water cooled tube 28 is installed under the motor housing fixing portion  24   c  and cooling water is circulated in the tube to efficiently cool the pump inside substrate  25 . By constructing a vacuum pump in this manner, the accumulation of solid product of process gas in the vacuum pump is restrained, and thus the pump inside substrate can be cooled efficiently.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vacuum pump and, more particularly, to a vacuum pump which is used when a process gas for, for example, a semiconductor manufacturing system is sucked and exhausted.

[0003] 2. Description of the Related Art

[0004] In recent years, a demand for semiconductor manufacturing systems has increased suddenly due to the widespread use of semiconductor devices such as memory and integrated circuit.

[0005] These, semiconductor devices are usually manufactured in a vacuum chamber in a high vacuum state for each process, and a vacuum pump is frequently used to evacuate the vacuum chamber.

[0006] The semiconductor device manufacturing processes include processes in which various kinds of process gases are applied to a substrate of semiconductor, so that the vacuum pump is used not only to evacuate the vacuum chamber but also to suck and exhaust these process gases.

[0007] These process gases are sometimes introduced into the chamber in a high-temperature state to enhance the reactivity. However, these process gases are cooled during exhaustion, and thereby a chemical reaction takes place to form a solid product, which may adhere and accumulate in the vacuum pump.

[0008] For example, when silicon chloride (SiCl₄) is used as a process gas for an aluminum etching apparatus, in a low-vacuum region of 760 [torr] to 10⁻² [torr] containing much water, the chemical reaction of silicon chloride is promoted, and thus aluminum chloride (AlCl₃) is precipitated as a solid product, and adheres and accumulates in the vacuum pump. In a low-temperature region of about 20° C., the chemical reaction of silicon chloride is further promoted.

[0009] In the vacuum pump, a rotor provided with a large number of rotor blades rotates at a high speed of several ten thousand revolutions per minute. If precipitates accumulate on a stator blade disposed on the inner peripheral surface of a casing of the vacuum pump, for example, a disadvantage of contact with the rotor blade may occur. Also, in some cases, the accumulated precipitates narrow a gas discharge path, which remarkably degrades the performance of vacuum pump.

[0010] Thereupon, methods for restraining the precipitation of solid product in the vacuum pump have so far been proposed.

[0011] Generally, there is used a method in which heating is performed from the outside to increase the internal temperature of vacuum pump, by which the adhesion of process gas is restrained. An example of this method is briefly explained with reference to a turbo-molecular pump shown in FIG. 2. A location at which the solid product of process gas is precipitated most easily in the turbo-molecular pump is a base 101 which has a high pressure and moreover is close to a water cooled tube 102 (for temperature control) Therefore, the base 101 is heated by using a heater 103 so as to be kept at a high temperature.

SUMMARY OF THE INVENTION

[0012] However, the above-described method using a heater presents a problem with a heat conduction path.

[0013] The conduction path of heat generated by the heater 103 is indicated by the arrow marks in FIG. 2. Thus, the heat generated by the heater 103 is transferred to a motor housing 106 and a pump inside substrate 104 through the base 101. Since a motor section 105 disposed in the motor housing 106 and the pump inside substrate 104 have a design limit temperature set considering reliability, the vacuum pump must be used in the setting value range of design limit temperature when the vacuum pump is operated. In particular, the design limit temperature of the pump inside substrate 104 is as low as 80° C.

[0014] Thus, in the conventional construction, if a heater is used for heating, the motor section and the pump inside substrate, which are not desired to be heated, are also heated.

[0015] Accordingly, an object of the present invention is to provide a vacuum pump in which the accumulation of solid product is restrained by keeping a discharge path for process gas in the vacuum pump at a higher temperature than before, and a motor and a pump inside substrate are cooled effectively.

[0016] To achieve the above object, the invention of a first aspect provides a vacuum pump including a body which has a casing and a base and is provided with a gas intake port and a gas discharging port; a rotor pivotally supported in the body so as to be rotatable; a motor for driving the rotor; a motor housing which is located in the body and is fixed to the base; gas transfer means, which is provided between the casing and the rotor, for transferring gas sucked through the gas intake port to the gas discharge port; heating means for heating a gas discharge path for the gas transferred by the gas transferring means; a pump inside substrate which is disposed in the base and the motor housing and is mounted with a predetermined circuit; and heat shutoff means for shutting off heat transfer from the base to the pump inside substrate and motor.

[0017] The heating means is composed of, for example, a heater disposed around the base or the casing or in the vacuum pump.

[0018] To achieve the above object, in the invention of a second aspect, the heat shutoff means is a heat shutoff wall integrally formed at the end on the base side of the motor housing, and the motor housing is fixed to the base via the heat shutoff means.

[0019] To achieve the above object, in the invention of a third aspect, the heat shutoff wall has a flange portion on the end face opposite to the motor housing, and the motor housing is fixed to the base via the flange portion.

[0020] To achieve the above object, in the invention of a fourth aspect, the vacuum pump further includes cooling means for cooling the motor housing.

[0021] To achieve the above object, the invention of a fifth aspect provides a vacuum pump including a body which has a casing and a base and is provided with a gas intake port and a gas discharging port; a rotor pivotally supported in the body so as to be rotatable; a motor for driving the rotor; a motor housing which is located in the body and is fixed to the base; gas transfer means, which is provided between the casing and the rotor, for transferring gas sucked through the gas intake port to the gas discharge port; heating means for heating a gas discharge path for the gas transferred by the gas transferring means; a pump inside substrate which is disposed in the base and the motor housing and is mounted with a predetermined circuit; and heat insulating means provided on the opposing surface of the motor housing and the base.

[0022] The heating means is composed of, for example, a heater disposed around the base or the casing or in the vacuum pump.

[0023] To achieve the above object, in the invention of a sixth aspect, the heat insulating means is a gap or a heat insulating material.

[0024] To achieve the above object, in the invention of a seventh aspect, the vacuum pump further includes heat shutoff means for shutting off heat transfer from the base to the pump inside substrate and motor.

[0025] To achieve the above object, in the invention of an eighth aspect, the cooling means is a water cooled tube provided on the motor housing to circulate cooling water.

[0026] To achieve the above object, in the invention of a ninth aspect, the water cooled tube is provided on the motor housing so that solder or a paste material for heat conduction is additionally provided.

[0027] According to the present invention, by isolating the motor housing and base from the surface of heat conduction, the pump inside substrate disposed in the motor housing can be protected from heating, caused by the heat generated by the heater. Also, by directly cooling the motor housing, the pump inside substrate can be cooled efficiently. Since the pump inside substrate can be cooled efficiently, the setting temperature of the gas discharge path in the vacuum pump can be increased as compared with the conventional vacuum pump, and thus the precipitation of solid product in the vacuum pump can be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a sectional view of a turbo-molecular pump in accordance with the present invention; and

[0029]FIG. 2 is a sectional view of a conventional turbo-molecular pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] A preferred embodiment of the present invention will now be described in detail with reference to FIG. 1.

[0031]FIG. 1 is a sectional view of a turbo-molecular pump in accordance with the present invention, showing a cress section in the axial direction of a rotor shaft 2.

[0032] Although not shown in FIG. 1, a gas intake port 3 of a turbo-molecular pump 1 is connected to a vacuum chamber of a semiconductor manufacturing system via a conductance valve (a valve for regulating conductance, i.e., flow ability of exhaust gas by changing the cross-sectional area of flow path of pipe) and the like, and a gas discharge port 4 is connected to an auxiliary pump.

[0033] A casing 5 that forms a casing for the turbo-molecular pump 1 has a cylindrical shape, and a rotor shaft 2 is disposed in the center thereof. The casing 5 constitutes a body 31 of the turbo-molecular pump 1 together with a base 6.

[0034] At the upper part, lower part, and bottom part in the axial direction of the rotor shaft 2, there are provided magnetic bearing portions 7, 8 and 9, respectively. The rotor shaft 2 is supported in the radial direction (radial direction of the rotor shaft 2) in a non-contact manner by the magnetic bearing portions 7 and 8, and is supported in the thrust direction (axial direction of the rotor shaft 2) in a non-contact manner by the magnetic bearing portion 9. These magnetic bearing portions 7, 8 and 9 constitute what is called a five-axis control type magnetic bearing, and the rotor shaft 2 has only the degree of freedom of rotation around the axis of the rotor shaft 2.

[0035] In the magnetic bearing portion 7, four electromagnets are arranged at 90° intervals around the rotor shaft 2 so as to be opposed to each other. The rotor shaft 2 is formed of a material with high magnetic permeability (for example, iron) , and hence is attracted by a magnetic force of the electromagnet.

[0036] A displacement sensor 10 detects displacement in the radial direction of the rotor shaft 2. When detecting displacement of the rotor shaft 2 in the radial direction from a predetermined position by means of a displacement signal sent from the displacement sensor 10, a control section, not shown, operates to return the rotor shaft 2 to the predetermined position by regulating the magnetic force of each electromagnet. Thus, the magnetic force of electromagnet is regulated by feedback controlling the exciting current of each electromagnet.

[0037] The control section carries out feedback control of magnetic force of the magnetic bearing portion 7 by means of a signal sent from the displacement sensor 10. Thereby, the rotor shaft 2 is magnetically levitated in the radial direction in the magnetic bearing portion 7 with a predetermined clearance being provided with respect to the electromagnets, and is held in a space in a non-contact manner.

[0038] The construction and operation of the magnetic bearing portion 8 are the same as those of the magnetic bearing portion 7.

[0039] In the magnetic bearing portion 8, four electromagnets are arranged at 90° intervals around the rotor shaft 2, and the rotor shaft 2 is held in the radial direction in the magnetic bearing portion 8 in a non-contact manner by a suction force of magnetic force of the electromagnets.

[0040] A displacement sensor 11 detects displacement in the radial direction of the rotor shaft 2.

[0041] Upon receipt of a displacement signal in the radial direction of the rotor shaft 2 from the displacement sensor 11, the control section, not shown, carries out feedback control of the exciting current of electromagnet so as to hold the rotor shaft 2 at a predetermined position by correcting the displacement.

[0042] The control section carries out feedback control of magnetic force of the magnetic bearing portion 8 by means of a signal sent from the displacement sensor 11. Thereby, the rotor shaft 2 is magnetically levitated in the radial direction in the magnetic bearing portion 8 with a predetermined clearance being provided with respect to the electromagnets, and is held in a space in a non-contact manner.

[0043] Thus, since the rotor shaft 2 is held in the radial direction at two places of the magnetic bearing portions 7 and 8, the rotor shaft 2 is held at the predetermined position in the radial direction.

[0044] The magnetic bearing portion 9 provided at the lower end of the rotor shaft 2 is composed of a disk-shaped metallic disk 12, electromagnets 13 and 14, and a displacement sensor 15, and holds the rotor shaft 2 in the thrust direction.

[0045] The metallic disk 12, which is formed of a material with high magnetic permeability such as iron, is fixed perpendicularly to the rotor shaft 2 in the center thereof. Above and below the metallic disk 12, the electromagnet 13 and the electromagnet 14 are provided respectively. The electromagnet 13 attracts the metallic disk 12 upward by means of the magnetic force, and the electromagnet 14 attracts the metallic disk 12 downward. The control section suitably regulates the magnetic force applied to the metallic disk 12 by the electromagnets 13 and 14 so that the rotor shaft 2 is magnetically levitated in the thrust direction and held in a space in a non-contact manner.

[0046] The displacement sensor 15 detects displacement in the thrust direction of the rotor shaft 2, and sends the detection signal to the control section, not shown. The control section detects displacement in the thrust direction of the rotor shaft 2 based on the displacement detection signal received from the displacement sensor 11.

[0047] When the rotor shaft 2 moves either way in the thrust direction and is displaced from a predetermined position, the control section operates so that the magnetic force is regulated by feedback controlling the exciting currents of the electromagnets 13 and 14 so as to correct the displacement, by which the rotor shaft 2 is returned to the predetermined position. The control section continuously carried out this feedback control so that the rotor shaft 2 is magnetically levitated in the thrust direction at the predetermined position and held there.

[0048] As described above, the rotor shaft 2 is held in the radial direction by the magnetic bearing portions 7 and 8, and is held in the thrust direction by the magnetic bearing portion 9. Therefore, the rotor shaft 2 has only the degree of freedom of rotation around the axis of the rotor shaft 2.

[0049] The rotor shaft 2 is provided with a motor section 16 between the magnetic bearing portions 7 and 8. In this embodiment, the motor section 16 is assumed to be formed of a dc brushless motor as an example.

[0050] In the motor section 16, a permanent magnet is fixed around the rotor shaft 2. This permanent magnet is fixed so that, for example, the N pole and S pole are arranged 180° apart around the rotor shaft 2. Around this permanent magnet, for example, six electromagnets are arranged at 60° intervals symmetrically and opposingly with respect to the axis of the rotor shaft 2 with a predetermined clearance being provided with respect to the rotor shaft 2.

[0051] Also, at the lower end of the rotor shaft 2, a rotational speed sensor, not shown, is installed. The control section, not shown, can detect the rotational speed of rotor shaft 2 based on the detection signal from the rotational speed sensor. Also, for example, near the displacement sensor 11, a sensor, not shown, is installed to detect the phase of rotation of the rotor shaft 2. The control section detects the position of the permanent magnet by using the detection signals of this sensor and the rotational speed sensor.

[0052] At the upper end of the rotor shaft 2, a rotor 17 is installed with a plurality of bolts 18.

[0053] As described below, a portion ranging from a substantially middle position of the rotor 17 to the gas intake port 3, that is, a substantially upper half portion in FIG. 1 is a molecular pump section, and a substantially lower half portion in the figure, that is, a portion ranging from a substantially middle position of the rotor 17 to the gas discharge port 4 is a screw groove pump section.

[0054] In the molecular pump section located on the gas intake port side of the rotor 17, rotor blades 19 are installed at a plurality of stages radially from the rotor 17 so as to be inclined through a predetermined angle from a plane perpendicular to the axis of the rotor shaft 2. The rotor blade 19 is fixed to the rotor 17 so as to be rotated at a high speed together with the rotor shaft 2.

[0055] On the gas intake port side of the casing 5, stator blades 20 are arranged toward the inside of the casing 5 alternately with the rotor blades 19 so as to be inclined through a predetermined angle from a plane perpendicular to the axis of the rotor shaft 2.

[0056] When the rotor 17 is driven by the motor section 16 and is rotated together with the rotor shaft 2, exhaust gas is sucked through the gas intake port 3 by the action of the rotor blades 19 and the stator blades 20.

[0057] The exhaust gas sucked through the gas intake port 3 passes between the rotor blade 19 and the stator blade 20, and is sent to the screw groove pump section formed in the lower half portion in the figure. At this time, the temperature of the rotor blade 19 is increased by friction between the rotor blade 19 and the exhaust gas and the conduction of heat generated in the motor section 16. This heat is transferred to the stator blade 20 by radiation or gas molecule of exhaust gas.

[0058] A spacer 21 is a ring-shaped member, and is formed of a metal such as aluminum, iron, stainless steel, copper, or an alloy containing these metals as components.

[0059] The spacer 21 is interposed between stages of the stator blades 20 to keep the stage formed by the stator blades 20 at a predetermined interval, and holds the stator blades 20 at predetermined positions.

[0060] The spacers 21 are connected to each other in the outer peripheral portion, and form a heat conduction path for conducting the heat that the stator blade 20 receives from the rotor blade 19 and the heat generated by friction between the exhaust gas and the stator blade 20.

[0061] The screw groove pump section formed on the gas discharge port side of the rotor 17 is composed of a rotor 17 and a screw groove spacer 22.

[0062] The screw groove spacer 22 is a cylindrical member formed of a metal such as aluminum, copper, stainless steel, or iron, or an alloy containing these metals as components, and has a plurality of spiral screw grooves 23 formed in the inner peripheral surface thereof.

[0063] The direction of spiral of the screw groove 23 is a direction such that when molecules of exhaust gas move in the rotation direction of the rotor 17, the molecules are transferred to the gas discharge port 4.

[0064] When the rotor 17 is driven and rotated by the motor section 16, the exhaust gas is transferred from the molecular pump section in the upper half portion in the figure to the screw groove pump section. The transferred exhaust gas is transferred toward the gas discharge port 4 while being guided by the screw groove 23.

[0065] A heater 29 is mounted on the outer peripheral surface of the base 6. The heater 29 is formed of an electrical heating member such as a Nichrome wire, and is supplied with electric power from a temperature controller, not shown. The heater generates heat when being supplied with electric power, and heats the base 6. By heating the base 6, the temperature in a gas discharge path for process gas is kept at a high temperature, and thus the precipitation of solid product in the pump is restrained.

[0066] In the embodiment of the present invention, the heater 29 is mounted on the outer peripheral surface of the base 6 to heat the interior of gas discharge path near the base 6, which meets the conditions (low temperature, high pressure) for easy precipitation of solid product of process gas. Therefore, even if the heater 29 is mounted on the outer peripheral surface of the casing 5, in which case the interior of gas discharge path can be heated, an effect of restraining the precipitation of solid product of process gas can be achieved. Also, the heater 29 can be incorporated directly in the turbo-molecular pump to heat the gas discharge path.

[0067] In a motor housing 24, there are arranged the motor section 16, the magnetic bearing portions 7, 8 and 9, and the displacement sensors 10, 11 and 15. Further, beneath the magnetic bearing portions 7, 8 and 9, there is disposed a pump inside substrate 25 which is mounted with circuits in which various types of information on the vacuum pump are recorded. The pump inside substrate 25 is formed with circuits in which pump operation time, error history, setting temperature for temperature control, etc. are stored. These circuits use a large number of semiconductor parts. Since the design limit temperature for the semiconductor part is set considering reliability, the semiconductor part must be used within the range of setting value of design limit temperature when the vacuum pump is operated. The design limit temperature is set at a value considering the guaranteed value of parts maker and a margin.

[0068] Although an example of a turbo-molecular pump using a magnetic bearing as a bearing has been described in the embodiment of the present invention, the present invention can also be applied to the case where, for example, a mechanical bearing is used.

[0069] Next, explanation is given by dividing the motor housing 24 (24 is a composite body of 24 a, 24 b and 24 c) into three portions of a conventional portion 24 a, a heat shutoff wall portion 24 b, and a fixing portion 24 c. For convenience of explanation, each portion of the conventional portion 24 a, heat shutoff wall portion 24 b, and fixing portion 24 c is indicated by different hatching.

[0070] The conventional portion 24 a, which is a portion corresponding to a motor housing 106 in FIG. 2, serves to support the motor.

[0071] The heat shutoff wall portion 24 b, which is a portion serving to shut off heat so that the radiation heat of the base 6 heated by the heater 29 does not transfer to the pump inside substrate 25, is formed into a cylindrical shape extending from the conventional portion 24 a in the downward direction of turbo-molecular pump.

[0072] The fixing portion 24 c, which is a portion used when the motor housing 24 is installed to the base 6, is formed into a flange shape on the lower end face of the heat shutoff wall portion 24 b. The fixing portion 24 c is also used when a back cover 26 for covering an opening at the bottom of the turbo-molecular pump is installed.

[0073] A gap portion 27 is formed by providing a gap between the motor housing 24 and the base 6. A gap portion 27 a is formed on the inner peripheral surface of the base 6 so as to decrease the contact area between the motor housing 24 and the base 6 as far as possible. A gap portion 27 b is formed similarly on the lower end surface of the base 6.

[0074] The gap portion 27 is provided to prevent the heat of the base 6 heated by the heater 29 from transferring to the motor housing 24, and serves to decrease the thermal conductivity between the base 6 and the motor housing 24.

[0075] The motor housing 24 is fixed to the base 6 with bolts with a heat insulating material 30 being interposed in the connecting portion. The heat insulating material 30 serves to prevent the heat of the base 6 heated by the heater 29 from transferring to the connecting portion.

[0076] The motor housing 24 is provided with cooling means for cooling the pump inside substrate 25 and the like in the motor housing 24.

[0077] Specifically, a water cooled tube 28 is installed under the motor housing fixing portion 24 c to circulate cooling water. Solder, a paste material for heat conduction, or the like can be provided additionally between the water cooled tube 28 and the motor housing fixing portion 24 c to efficiently conduct cooling.

[0078] Also, a cooling tube can be run directly in the motor housing to cool the motor housing 24.

[0079] The process gas sucked through the gas intake port 3 moves in the gas discharge path toward the gas, discharge port 4 while the temperature thereof decreases. However, since the base 6 is heated by the heater 29, the process gas can be prevented from adhering and accumulating near the base 6 as a solid product.

[0080] Also, since the motor housing 24 is thermally insulated from the base 6 by the gap portion 27 and the heat insulating material 30, the motor housing 24 is not heated by the heat of the base 6 heated by the heater 29, and the heat can be transferred efficiently to cooling water circulating in the water cooled tube 28. 

What is claimed is:
 1. A vacuum pump comprising: a body which has a casing and a base and is provided with a gas intake port and a gas discharging port; a rotor pivotally supported in said body so as to be rotatable; a motor for driving said rotor; a motor housing which is located in said body and is fixed to said base; gas transfer means, which is provided between said casing and said rotor, for transferring gas sucked through said gas intake port to said gas discharge port; heating means for heating a gas discharge path for the gas transferred by said gas transferring means; a pump inside substrate which is disposed in said base and said motor housing and is mounted with a predetermined circuit; and heat shutoff means for shutting off heat transfer from said base to said pump inside substrate and motor.
 2. The vacuum pump according to claim 1, wherein said heat shutoff means is a heat shutoff wall integrally formed at the end on the base side of said motor housing, and said motor housing is fixed to said base via said heat shutoff means.
 3. The vacuum pump according to claim 2, wherein said heat shutoff wall has a flange portion on the end face opposite to said motor housing, and said motor housing is fixed to said base via said flange portion.
 4. The vacuum pump according to 1, wherein said vacuum pump further comprises cooling means for cooling said motor housing.
 5. The vacuum pump according to 2, wherein said vacuum pump further comprises cooling means for cooling said motor housing.
 6. The vacuum pump according to 3, wherein said vacuum pump further comprises cooling means for cooling said motor housing.
 7. The vacuum pump according to claim 4, wherein said cooling means is a water cooled tube provided on said motor housing to circulate cooling water.
 8. The vacuum pump according to claim 5, wherein said cooling means is a water cooled tube provided on said motor housing to circulate cooling water.
 9. The vacuum pump according to claim 6, wherein said cooling means is a water cooled tube provided on said motor housing to circulate cooling water.
 10. A vacuum pump comprising: a body which has a casing and a base and is provided with a gas intake port and a gas discharging port; a rotor pivotally supported in said body so as to be rotatable; a motor for driving said rotor; a motor housing which is located in said body and is fixed to said base; gas transfer means, which is provided between said casing and said rotor, for transferring gas sucked through said gas intake port to said gas discharge port; heating means for heating a gas discharge path for the gas transferred by said gas transferring means; a pump inside substrate which is disposed in said base and said motor housing and is mounted with a predetermined circuit; and heat insulating means provided on the opposing surface of said motor housing and said base.
 11. The vacuum pump according to claim 10, wherein said heat insulating means is a gap or a heat insulating material.
 12. The vacuum pump according to claim 10, wherein said vacuum pump further comprises heat shutoff means for shutting off heat transfer from said base to said pump inside substrate and motor.
 13. The vacuum pump according to claim 11, wherein said vacuum pump further comprises heat shutoff means for shutting off heat transfer from said base to said pump inside substrate and motor.
 14. The vacuum pump according to claim 12, wherein said heat shutoff means is a heat shutoff wall integrally formed at the end on the base side of said motor housing, and said motor housing is fixed to said base via said heat shutoff means.
 15. The vacuum pump according to claim 13, wherein said heat shutoff means is a heat shutoff wall integrally formed at the end on the base side of said motor housing, and said motor housing is fixed to said base via said heat shutoff means.
 16. The vacuum pump according to claim 14, wherein said heat shutoff wall has a flange portion on the end face opposite to said motor housing, and said motor housing is fixed to said base via said flange portion.
 17. The vacuum pump according to claim 15, wherein said heat shutoff wall has a flange portion on the end face opposite to said motor housing, and said motor housing is fixed to said base via said flange portion.
 18. The vacuum pump according to claim 10, wherein said vacuum pump further comprises cooling means for cooling said motor housing.
 19. The vacuum pump according to claim 18, wherein said cooling means is a water cooled tube provided on said motor housing to circulate cooling water.
 20. The vacuum pump according to claim 19, wherein said water cooled tube is provided on said motor housing so that solder or a paste material for heat conduction is additionally provided. 